<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #result {
      width: 200px;
      height: 100px;
      border: 1px solid #90b
    }
  </style>
</head>
<body>
  <div id="result"></div>



  <script>
    const result = document.getElementById('result')
    result.addEventListener('mouseover', function ()  {
        // 1.创建对象
        const xhr = new XMLHttpRequest()

        // 2.初始化
        xhr.open('POST', 'http://127.0.0.1:8000/server')

        //设置请求头  名字 值  Content-Type设置请求体内容的类型
        xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded') 
        // 自定义头,需要后端改头 信息 response.setHeader('Access-Control-Allow-Headers', '*')
        xhr.setRequestHeader('name', 'atguigu') 



        // 3.发送
        // xhr.send('a=100&b=200&c=300')
        xhr.send('a:100&b:200&c:300')

        // 4.事件绑定
        xhr.onreadystatechange = function () {
          // 判断
          if(xhr.readyState === 4 ) {
            if(xhr.status >= 200 && xhr.status < 300) {
              // 处理服务端返回结果
              result.innerHTML = xhr.response
            }
          }
        }
    })
  </script>







</body>
</html>